Thanks to all for your helpful input, especially GHG and Gremlin. I now have 5 areas for experimentation, not necessarily in sequence, after laying down a repeatable baseline test run for comparison:
1. Try a dose of Techron in a tank of E-10,
2. Try a tank of straight gas (located a source nearby),
3. Advance the TPS idle output voltage,
4. Tweak with the idle air bypass screw, and
5. Try temporarily disabling the lambda sensor.
Are there potentially harmful downsides to #5? If, as Ekatus thinks, the ECU control strategy on lambda is simply to control emissions, I would think I could test this case for impact on my problem (engine stumble upon throttling up from idle) without harm. If, as Gremlin says, the ECU is using lambda feedback to keep nudging the AFR just barely lean of stoiciometric, then disabling the sensor might cause the ECU to drive the fuel pump output to the limit of the map range, one way or the other (max or min) - much smoke or knocka-knock?
I appreciate your further input on this, and I will post my experimental findings as I make them - now that last night's snow is gone!